“However, imagine if you needed to replace the battery in your car, but you could only buy the battery from the dealership, and only they could install it, even if you could easily replace it yourself. That sounds ridiculous!” -
This is exactly what is happening, cars particularly with stop start need the battery coded to the car, and the alerts regarding not having stop/start enabled removed. Unfortunately, your cheap and cheerful code reader isn’t going to cut it, so the only answer is to take it to a repair centre that has the right diagnostics to do this. Yes, VW, I’m talking about you!!!!